1. Field of the Invention
This invention relates to a reverse rotation preventing device for a Diesel engine for use with a construction equipment such as a hydraulic shovel or a hydraulic crane.
2. Description of the Prior Art
In a construction equipment wherein a hydraulic pump is driven by a Diesel engine, when the load to the pump increases beyond the torque of the engine, the engine is sometimes reversed, which may give rise to seizure of or damage to the engine.
Conventionally, reverse rotation preventing devices for a Diesel engine are roughly divided into two types including a first type wherein a stopping signal for an engine is developed after occurrence of reverse rotation of the engine and a second type wherein a stopping signal for an engine is developed upon stopping of forward rotation of the engine, that is, immediately before starting of reverse rotation of the engine. An exemplary one of known reverse rotation preventing devices of the former type includes a check valve (butterfly valve) interposed, for example, in an intake air passage of the engine for closing the intake air passage when the flow of air is reversed by reverse rotation of the engine. On the other hand, an exemplary one of known reverse rotation preventing devices of the latter type is constituted such that, when, for example, forward rotation of the engine is stopped, an actuating solenoid for an engine stopping lever is energized to operate the lever to stop the engine in response to an action of a pressure switch provided for detecting a pressure of lubricating oil of the engine.
However, with the reverse rotation preventing device of the former type, since reverse rotation itself of the engine is detected, the anticipated object of prevention of reverse rotation of the engine cannot substantially be attained. On the other hand, also with the reverse rotation preventing device of the latter type, reverse rotation actually takes place because there is some time lag or delay in response between a point of time when the engine is stopped and another point of time when such stopping of the engine is detected.
Where the reverse rotation preventing device of the latter type is constituted such that, each time forward rotation of the engine is stopped, the engine is interlocked in an engine operation stopping condition, means are required for releasing such interlock when the engine is to be subsequently started. For example, where the interlock is provided by operation of such an actuating solenoid for an engine stopping lever as described above, it is necessary to additionally provide a circuit for deenergizing the solenoid in response to a starting signal of the key switch of the engine. Consequently, the reverse rotation preventing device is complicated in construction and is thus deteriorated in reliability as much. Further, since the solenoid is kept in an energized condition during such interlock, several disadvantages such as the discharge of a battery, the deterioration of the life of the solenoid, and so forth are created.